Sunday, August 11, 2013

Saab's two-stroke heritage

In the world of streamlined cars, few have been as efficient or built with such singularity of purpose as the Saab. That the car should have demonstrated such aerodynamic qualities should come as no surprise when one considers Saab, the Swedish Aeroplane Company Limited (Svenska Aeroplan AB) was first and foremost an aircraft manufacturer.

Sweden had long pursued a strict policy of neutrality in European affairs, but with Europe sliding slowly towards the Second World War, the government recognised the need to develop military self sufficiency. In 1937 the Svenska Aeroplan AB was established to build military aircraft. Their first project was the Saab 17 fighter-bomber, which took to the air in 1940. The Saab 17 would remain in service until 1955. Saab went on to build single and multi-engined fighters and bombers throughout the war years and by the end of the war were experimenting with jet aircraft.

As the Second World War drew towards its close, Saab's management recognised that there would be little post-war demand for their aircraft and began casting around for an alternative business opportunity. After considering a venture into the exciting world of fitted kitchens, they decided to investigate motor vehicles. Ironically however, almost no one at Saab knew much about motor cars. In fact, in the twenty man team assigned to the project, only three had a drivers license.

Project 92, led by engineer Gunnar Ljungström, commenced in 1945 in the greatest secrecy. To provide the team with some practical experience with motor vehicles several pre-war German cars were purchased for study. These included a DKW F8, a Hanomag, an Opel Kadet and a Volkswagen. Although the team didn't really know how to go about building a car, there was absolute clarity about what that car should be - it would be a budget car, costing less than 3200 Swedish Kroner, economical to run, modern and streamlined.

Ljungström turned to a former Saab employee, Sixten Sason, for the styling of the car. Sason had left Saab in the 1940s to become a futurist illustrator and he sketched out a number of futuristic design concepts, one of which was eventually turned into a 1/10th wooden model for wind tunnel testing. The testing returned an outstanding drag co-efficient of 0.32. In April 1946 a full scale wooden model was built for presentation to Saab management. The wooden body was coated in black shoe polish in lieu of paint. The response from management however wasn't as positive as the project team would have liked, but Ljungström's response has gone down in Saab legend "...if it can save 100 litres of fuel a year, it doesn’t matter if it looks like a frog."

Because look like a frog it did. This photo of the first test car was taken at Saab's Linkoping factory and airfield.  The car would undergo significant modification.

Ljungström's view prevailed and the project pressed ahead. The next step was to build a functioning car; something Saab were still struggling with. A decision had been made to use a two-stroke engine but the design of the engine had not yet been finalised. Nor had the car's ladder chassis been built or tested, so a working mock up was constructed using a DKW F8 chassis and 688cc engine with a hand beaten steel body-shell. This became the Ursaab - the first Saab.

Saab's decision to use a two-stroke engine is often attributed to their unconventional and idiosyncratic approach to automobile design, but it was nothing of the sort. Firstly, two-stroke engines were simpler to build, having fewer moving parts than a four stroke, and were therefore well suited for a budget vehicle. Secondly, in terms of power output to size, two-strokes substantially outperformed four-strokes, and they were more economical to run in terms of fuel consumption and maintenance. Lastly, because two-stroke engines were lubricated through their fuel system and did not rely on oil sumps and pumps, they could be trusted to start even during Sweden's sub-zero winters.

Inside the engine bay of Saab 920001. The petrol tank comes directly from a DKW F8 and is stamped with the four rings logo of Auto-Union.

Under conditions of top secrecy the car underwent road testing. Although the first car was more DKW than Saab, there were lots of lessons to be learnt from the testing. By mid 1946 Saab's two-stroke engine was finally ready and was swapped into the car. Saab's two-stroke was based on DKW's trusty design and included a DKW style freewheel. The engine was a two cylinder 748cc engine delivering 25 horsepower and was mounted transversely driving the front wheels through a three-speed gearbox.

Four more prototypes were built and subjected to rigorous testing under the most trying of conditions, bashing through the trackless Swedish forests in all seasons. The cars survived their mistreatment and in 1947 Saab began adapting their Trollhatten factory to automobile production.

The lessons from the Ursaab testing were incorporated into design of the production vehicle. The fully enclosed wheel arches, which were a key feature of the Ursaab's aerodynamic streamlining, were dropped. In driving conditions they had proved to be a snow, sleet and mud trap. The steel bodywork was also found to be too heavy, especially on the doors. This was the result of Saab's unusual technique of stamping the entire body in a single pressing. The doors and bonnet were then cut from the pressing. Doors and bonnets were lightened and the bonnet and front-end was restyled and widened to allow easier removal of the engine. The bonnet was also hinged from the front instead of the rear in the Ursaab. Suspension was via Volkswagen style torsion bars.

Saab 92

Almost five years after Saab first initiated the Saab 92 car project, the car went on sale on 10 June 1949. The car came in only one colour - dark green; the paint was surplus from Saab's aircraft factory. 700 cars were built in the first year but production quickly ramped up and 20,000 had been built by the time production ceased in 1956.

Saab 93

In 1956 the Saab 92 was replaced by the Saab 93. Nicknamed the 'bullnose' because of its distinctive radiator styling, the car featured a new three-cylinder 748cc two-stroke engine. Although of no greater cubic capacity than the earlier two cylinder engine it was a better engine and developed 33 horsepower. The engine was longitudinally mounted but still had only three gears. To fit beneath the bonnet the engine was rotated some 15 degrees from upright.

Saab 96

Some 56,000 Saab 93's were built until the car was replaced by the Saab 96 in 1960. The new car was virtually identical to its predecessor baring minor improvements and changes to the instrumentation. In 1963 the 748cc engine was replaced with an 841cc engine developing 42 horsepower.

By 1965 two-stroke engines were generally viewed as old fashioned by the motoring public and Saab's sales began to ebb. Like DKW, Saab had built its name and fortune on its two-stroke engine and within the company there was strong resistance to changing the engine, especially from management who did not relish the cost to develop a new engine while Saab was enjoying outstanding success in racing and rallying. Nevertheless, the automobile department could see the writing on the wall and initiated a secret project to replace the two-stroke engine. Several different engines were trialled in secret locations around the country and in 1967 the new 95 V4 was released with a Ford Taunus V4 four stroke engine, bringing an end to Saab's two-stroke heritage.

All the two-stroke Saab's won fame in racing and rallying, but that's worth an article all to itself.


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1 comment:

  1. Now with all that biofuels trend, sometimes I wonder if 2-stroke engines could come back to the mainstream automotive market because a viable replacement for petroleum-based oils is already available for a long time, those Castor-based oils mainly used in kart-racing. And their layout has its advantages too, most notably less weight, easy fitment even in the tight engine bays of newer compact cars, less internal frictions due to the absence of a valvetrain, and there is also the direct injection developed by the Australian company Orbital Engines well-proven in the marine motor industry and in motorcycles. There are even some independent researchers trying to develop a 2-stroke engine with a lube system similar to the currently mainstream 4-stroke ones, which doesn't seem to be a bad idea at all, altough I'm still more favorable to the traditional lube method.